DEVELOPING NOVEL THERAPIES FOR ALZHEIMER'S DISEASE TARGETING BRAIN PHOSPHOLIPID DYSREGULATION

Abstract

Synaptojanin 1 (synj1), the main phosphoinositol biphosphate (PIP2) degrading enzyme in the brain, has been recently linked to AD. It has been shown that synj1 regulates lysosomal clearance of Aβ, and that increased synj1 expression is linked to ApoE4-induced cognitive deficits. Moreover, it has been found that reduction of synj1 ameliorates blast-induced tau hyper-phosphorylation. Together, these studies suggest that reduction of synj1 has multiple benefits for AD. To test if reduction of synj1 with a resultant elevation of brain PIP2 levels is a feasible therapeutic strategy for AD, a screening of a library of compounds with the potential to reduce synj1 protein levels was performed. Based on “The Connectivity Map”, 89 small molecules were selected for further analysis of synj1 and Aβ-lowering effects using wild-type and ApoE4 neuronal cultures. The identified lead compound nimodipine was further tested in vivo using an AD transgenic mouse model (APPSwe/PS1ΔE9), and in an ApoE4 KI mouse model. Medicinal chemistry modifications of nimodipine were performed to develop analogs with increased potency at lowering synj1. An FDA-approved drug nimodipine reduced synj1 protein and Aβ levels both in vitro and in vivo. It also improved cognitive function in AD mouse models in short-term treatment. However, chronic administration of nimodipine failed to reduce brain Aβ42 levels (particularly insoluble fractions), or to improve cognitive function. Using medicinal chemistry, structural analogs of nimodipine were developed with reduced calcium channel activity and increased efficacy at improving cognitive function in vivo. One first-generation analog SynaptoCpd#9, exhibited an attenuated inhibition of calcium channels and an increased potency against synj1 and Aβ42 compared to nimodipine both in vitro and in vivo. Oral administration of SynaptoCpd#9 in APPSwe/PS1ΔE9 and ApoE4 mice for 3–6 months improved cognitive function and reduced AD-related pathologies (insoluble Aβ42 particularly). RNA-sequencing and qPCR studies of treated ApoE4 neurons identified three candidate genes involved in nimodipine- or SynaptoCpd#9-mediated effects. A novel target, synj1, for AD has been identified with several benefical effects of reducing its expression characterized. Novel chemical scaffolds with medicinal chemistry modifications targeted at synj1 expression are developed toward preclinical drug candidates for AD.